Function validate_fixtures_semantic 

pub fn validate_fixtures_semantic(
    fixtures: &[Fixture],
    e2e_config: &E2eConfig,
    languages: &[String],
) -> Vec<ValidationError>

Perform semantic validation on loaded fixtures against e2e configuration.

Checks for:

1. Fixtures skipped for all languages (empty skip.languages)
2. Unknown call references not in [e2e.calls.*]
3. Categories where all fixtures are skipped (produces 0 test functions)
4. Missing required input fields for the resolved call config